Studies on graphene based poly (methyl methacrylate) nanocomposites

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STUDIES ON GRAPHENE BASED POLY(METHYL METHACRYLATE) NANOCOMPOSITES

SANDEEP NATH TRIPATHI

CENTRE FOR POLYMER SCIENCE AND ENGINEERING INDIAN INSTITUTE OF TECHNOLOGY DELHI

APRIL 2015

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© Indian Institute of Technology Delhi (IITD), New Delhi, 2015

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STUDIES ON GRAPHENE BASED POLY(METHYL METHACRYLATE) NANOCOMPOSITES

by

SANDEEP NATH TRIPATHI

Centre for Polymer Science and Engineering

submitted

in fulfilment of requirements of the degree of Doctor of Philosophy

to the

INDIAN INSTITUTE OF TECHNOLOGY DELHI

APRIL 2015

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Dedicated to my parents Shri Haridwar Nath Tripathi

&

Smt. Ramrati Devi

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CERTIFICATE

This is to certify that thesis entitled “Studies on Graphene Based Poly(methyl methacrylate) Nanocomposites” being submitted by Mr. Sandeep Nath Tripathi to the Indian Institute of Technology, Delhi, for the award of degree of Doctor of Philosophy is a record of bonafide research carried out by him. Mr. Sandeep Nath Tripathi has worked under my supervision and has fulfilled the requirements for the submission of this thesis, which to my knowledge has reached the requisite standard.

The results contained in this thesis are original and have not been submitted, in part or full, to any other University or Institute for the award of any other degree or diploma.

Date: Dr. Veena Choudhary

Place: Professor

Centre for Polymer Science & Engineering Indian Institute of Technology, Delhi Hauz Khas, New Delhi-110016

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ACKNOWLEDGEMENTS

This thesis could have not been completed without the generosity and support of many. First of all I wish to express my heartiest gratitude to my supervisor, Prof (Mrs) Veena Choudhary for her invaluable guidance and constant encouragement. Her caring attitude like mother and co-operation has been monumental throughout my research. Through her wealth of knowledge, direction and leadership I have been able to expand my knowledge in many areas of polymer science.

I express my sincere thanks to Prof S.N. Maiti, Prof A.K. Ghosh, Dr Josemon Jacob, Dr B.K.

Satapathy and Prof Manjeet Jassal for their constant encouragement, advice and support throughout my research work.

My special thanks to Mr Surender Kumar Sharma, Mr Shivkant, Mr Ashok Kapoor, Mr Virender Kumar Sharma (from glass blowing workshop), Mr Keshav Dev and Mr Alok Yadav (from NMR lab), Mr D.C. Sharma and Mr Kuldeep Sharma (from SEM lab) and office staff Ms Shalini, Sudhir, Raj and Pramod for their immediate help whenever needed.

I express my thanks to Prof B.D. Gupta from Physics Department, IIT Delhi, Dr S.K.

Dhawan and Dr R.B Mathur of National Physical Laboratory Delhi, India for providing facilities to carry out experiments in their lab.

Nothing could have been accomplished without my family support. I would like to extend my special gratitude to my family for their love, support and encouragement. I am extremely thankful to my brothers Mr Dilip Nath Tripathi and Mr Amrendra Nath Tripathi for their constant encouragement and emotional support throughout my career.

I am extremely thankful to all my friends and colleagues Mr. Rajender Singh Malik, Mr Harjeet Singh Jaggi, Mrs Meenakshi Verma, Mr Pawan Verma, Ms Bhavna Sharma, Mrs Shilpi Sharma, Mrs Savita Meena, Mrs Bindu Manchanda, Mrs Achla Tripathi, Mr Debanga Konwar, Mr Sampat S. Chauhan, Mr Vishwa Pratap Singh, Ms Banpreet Kaur, Ms Pragati,

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Mrs Priyanka Singh, Mrs Manisha Tomar, Dr Hemlata, Mr Rajendra Singla, Mr Abhishek Kumar, Mr Tahir Zafar and Mr Devendra Mogha and also my seniors Dr Bhanu P. Singh, Dr Parveen Saini, Dr Deeksha Gupta, Dr Anju Gupta, Dr Pravin Kumar Srivastav, Dr Shveta Mahajan and Dr Prabhat Garg.

I am also thankful to friends from other departments Dr Deepak Tripathi, Dr Navin Kumar Dwivedi, Dr Gaurav Kumar Singh (IAS), Dr Udit Kumar Soni, Dr Vinod Kumar, Mr Satyendra Kumar Mishra, Mr Manu Dalela, Mr Dinesh Shukla, Mr Abhishek Gandhi and Mr Vineet Chaudhary.

My dear friends Dr Anupam Gupta, Mr Narendra Kumar Mishra, Mr Alok Agrahari, Mr Ashwani Kumar Singh, Dr Deepak Kumar Yadav, Mr Upendra Pratap Singh and Mr Parvej Alam are greatly thanked for being an incredible support system and their encouraging words throughout my PhD.

I gratefully acknowledge University Grant Commission (UGC), India for providing Junior and Senior Research Fellowships.

Finally, I thank the ‘ALMIGHTY GOD’ for his blessings and further seek him to provide me blessings, patience and strength to accomplish newer goals.

Sandeep Nath Tripathi

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ABSTRACT

Over the last two decades polymer nanocomposites have been the subject of intense research interest in academia and industry which is spawned by advances such as the discovery of spherical fullerenes and carbon nanotubes. Graphene has been incorporated into various types of polymer matrices due to the exceptionally unique combination of properties such as high electrical and thermal conductivity, high surface area, strength toughness and stiffness. It was therefore expected that the incorporation of graphene into the polymer matrices will improve its mechanical, electrical, thermal and gas barrier properties. A number of thermosetting and thermoplastics have been used as matrix for the preparation of graphene/polymer nanocomposites and poly(methyl methacrylate) [PMMA] is one of them. It is used because of its some specific advantages such as low cost, optical clarity, ease of melt processibilty, mould-ability mostly into any shape, good weather-ability and good physico- chemical properties. The present study was carried out to investigate the effect of reduced graphene oxide (RGO)/graphene-carbon nanotubes (GCNT) content and its method of incorporation on the properties of PMMA. These composites were characterized for thermal, electrical, mechanical, rheological, morphological properties and evaluated as gas sensor based on surface plasmon resonance utilizing fiber optic probe.

The thesis has been divided into six chapters. Chapter 1 deals with the brief introduction of polymer nanocomposites and various nanofillers of carbon family along with detailed study of graphene followed by comprehensive literature review on the synthesis, characterization and applications of graphene in the field of polymer composites. It also reviews the different processing techniques used to fabricate polymer nanocomposites and their characterization [thermal, mechanical and electrical properties]. The basics of gas

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sensors based on surface plasmon resonance utilizing fiber optic probe, the role of graphene and PMMA have also been included in this chapter.

The detailed experimental methods used for the preparation of reduced graphene oxide (RGO)/graphene-carbon nanotube (GCNT) hybrids and PMMA/RGO or PMMA/GCNT composites are given in chapter 2 of thesis. The different techniques used for characterization and evaluation of the properties of PMMA/RGO or PMMA/GCNT composites are also described in this chapter.

The effect of reduced graphene oxide content and its method of incorporation by three methods on the properties of PMMA in PMMA/RGO composites are given in chapter 3. The interaction of RGO with PMMA matrix was investigated using FT-IR, Raman spectroscopy and also by X-ray diffraction analysis. The effect of RGO content on thermal, mechanical and electrical properties of PMMA/RGO nanocomposites fabricated by three different techniques, i.e. (i) in situ polymerization of MMA in presence of RGO (ii) in situ polymerization of MMA in presence of RGO and commercial PMMA beads and (iii) in situ polymerization of MMA in presence of RGO followed by sheet casting; up to 2.0 wt% RGO loading was investigated and the results are summarized in this chapter. Thermal stability of PMMA enhances upon incorporation of RGO in PMMA matrix irrespective of the methods.

However, the mass loss in first step, which may be due to the weak linkages such as head to head linkages decreased in case of sheet casting method as compared to other two methods. It was found that for a given RGO content, all three samples give different electrical conductivity highlighting the importance of compounding method. It was found that, conductivity of composites at 0.5 wt% RGO was 3.8×10^-6 S/cm (for in situ polymerized), 4.1×10^-6 S/cm (for in situ polymerized in presence of PMMA beads) which is ~ 5-order higher than neat PMMA (2.4×10^-11 S/cm) and 9.5×10^-5 S/cm (for samples prepared by sheet

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casting method) i.e. 6-orders higher of magnitude than PMMA. The mechanical properties of PMMA/RGO showed that addition of RGO leads to improvement of modulus which indicates the increase in stiffness of the composite. Further, the tensile strength of composites show that addition beyond 1 wt% loading of RGO, leads to deterioration of mechanical strength that can be attributed to the filler agglomeration effect and poor stress transfer characteristics. The elongation decreased with increasing RGO content indicating brittle fracture of composites. These studies clearly show that all the properties were better in case of sheet casting method and hence for further studies (i.e. for melt rheology and gas sensing behaviour) all the samples were prepared using sheet casting technique.

Chapter 4 includes the preparation and characterization of graphene-CNT (GCNT) hybrid filler via chemical method for nanocomposite application by varying the weight ratio of graphene and CNT i.e. 1:2, 1:1 and 2:1 and designated as GCNT-1, GCNT-2 and GCNT-3 respectively. The composites based on these fillers at fixed concentration (1 wt%) were prepared to investigate the effect of hybrid filler nature on the properties. On the basis of thermal and electrical properties, composites based on GCNT-2 filler showed better properties as compared to composites prepared using GCNT-1 and GCNT-3. Therefore for further studies GCNT-2 have been used to prepare PMMA/GCNT nanocomposites using varying amounts of GCNT-2 and evaluated as gas sensor.

Chapter 5 describes the evaluation of PMMA nanocomposites based on RGO/GCNT as gas sensors using surface plasmon resonance technique utilizing fiber optic probe. For the study of sensing performance of PMMA composites based on RGO/GCNT, chapter 5 was divided into two subchapters. In chapter 5A, we investigated the effect of RGO content on sensing behaviour. The probe was fabricated using a 24 cm length of plastic clad silica optical fibre of core diameter 600 µm and numerical aperture 0.4. About 1 cm length of

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cladding was removed from the middle portion of the fibre followed by washing with acetone and then a Cu layer of 40 nm was coated using thermal evaporation technique. The sensing layer was then deposited over the Cu layer by dip coating method. In the first part PMMA/RGO nanocomposites were evaluated for gases like NH₃, H₂S, Cl₂, H₂ and N₂ where the composites show selectivity mainly for NH3 gas. It was also found that as RGO loading increased in PMMA/RGO composite, shift in the resonance wavelength increases and a maximum shift of 35 nm at 5 wt% RGO loading in PMMA was observed. The second part of this chapter (chapter 5B) deals with the sensing performance of PMMA/GCNT nanocomposites for CH₄, NH₃, H₂S, CO₂, Cl₂, H₂ and N₂ where nanocomposite showed selectivity for methane gas. The maximum shift of 30 nm was observed at 5 wt% GCNT loading for PMMA/GCNT nanocomposite.

The final summary and conclusions of the thesis are given in chapter 6. Suggestions for future work are also included in this chapter.

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List of Figures

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Figure 1.1: Molecular structure of graphene as sp² hybridized chicken wire pattern

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Figure 1.2: Graphene as building block of all graphitic forms 4 Figure 1.3: Schematic diagram of growth of graphene on SiO2 substrates in

CVD process

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Figure 1.4: Schematic diagram of D.C. arc discharge set up 7 Figure 1.5: Pictorial representation for sequential unzipping of a carbon

nanotube to graphene nanoribbons

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Figure 1.6: Schematic representation from graphite to graphite oxide. 9 Figure 1.7: Schematic representation of reduction of graphite oxide to

reduced graphene oxide

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Figure 1.8: Sheet of graphene rolled to show formation of different types of single walled carbon nanotube

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Figure 1.9: Schematic of the formation of PMMA/GO nanocomposite by ATRP

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Figure 2.1: Chemical structure of AIBN, MMA monomer and PMMA 31 Figure 2.2: Schematic for the preparation of graphene oxide (GO) and

reduced graphene oxide (RGO)

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Figure 2.3: Schematic representation for the preparation of GCNT hybrid filler

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Figure 2.4: Mechanism for the catalysis of DMF in chlorination 34 Figure 2.5: Pictorial view of PMMA/RGO nanocomposites preparation

method (1) in-situ (2) in presence of PMMA beads and (3) sheet

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casting 35

Figure 2.6: Schematic for the fabrication of PMMA/GCNT hybrid composites

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Figure 2.7: Experimental set up of SPR probe for gas sensing utilizing optical fiber

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Figure 3.1: X-ray diffraction patterns of graphite, graphene oxide (GO) and reduced graphene oxide (RGO)

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Figure 3.2: SEM-EDX images of (a) graphene oxide (GO) and (b) reduced graphene oxide (RGO)

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Figure 3.3: (a) SEM (b) TEM and (c) AFM images of RGO 56 Figure 3.4: FTIR spectra of (a) graphite, (b) graphene oxide (GO), (c)

graphene (RGO), (d) PMMA and (e) PMMA/RGO composite (1 wt%)

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Figure 3.5: Raman spectra of (a) graphite (b) GO (c) RGO (d) PMMA/RGO (1 wt%) and (e) PMMA/RGO composite (2 wt%)

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Figure 3.6: XRD patterns of GO, RGO, PMMA and PMMA/RGO composites (2 wt%) and (1 wt%)

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Figure 3.7: Effect of RGO content on the electrical conductivity of PMMA/RGO nanocomposites

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Figure 3.8: TG traces of (a) graphite, graphene oxide (GO) and RGO; RGO and PMMA/RGO composites (b) in situ method (c) in presence of PMMA beads (d) sheet-casting method

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Figure 3.9: Plot of storage modulus (Eʹ) vs temperature for PMMA/RGO composites prepared by three methods [In situ- Method 1;

PMMA Beads- Method 2 and PMMA/RGO- Method 3]

66

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Figure 3.10: Plot of loss modulus (Eʹʹ) vs temperature for PMMA/RGO composites prepared by three methods [In situ- Method 1;

PMMA Beads- Method 2 and PMMA/RGO- Method 3]

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Figure 3.11: Variation of (a) tensile modulus (b) tensile strength and (c) strain at break with RGO content

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Figure 3.12: SEM images of (a) fracture surface of PMMA; PMMA/RGO nanocomposite (1 wt%) (b) in situ (c, d) in presence of PMMA beads, (e, f) Sheet casting

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Figure 3.13: HRTEM images of RGO (a, b) PMMA/RGO composite (1 wt%) (c, d) in situ (e, f) sheet casting

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Figure 3.14: Amplitude sweep test of PMMA and PMMA/RGO nanocomposites

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Figure 3.15: Plots of (a) storage modulus (Gʹ) (b) loss modulus (Gʹʹ) and (c) complex modulus (G٭) of PMMA/RGO nanocomposites as a function of frequency

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Figure 3.16: Plots of Gʹ, Gʹʹ vs frequency for PMMA/RGO nanocomposites 76 Figure 3.17: Complex viscosities as a function of (a) frequency and (b) RGO

content for PMMA/RGO nanocomposites

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Figure 3.18: SEM and TEM of PMMA/RGO nanocomposites (a, d) 0.5 wt%

(b, e) 2.0 wt% (c, f) 5.0 wt%

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Figure 4.1: IR spectra of (a) CNT-COOH (b) GO (c) RGO (d) GCNT-1 and (e) GCNT-2

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Figure 4.2: Raman spectra of (a) GO (b) CNT-COOH (c) RGO (d) GCNT-1 and (e) GCNT-2

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Figure 4.3: X-ray diffraction pattern of GO, RGO, MWCNT, GCNT-1 and 89

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Figure 4.4: SEM micrographs of (a) RGO (b) MWCNT (c) GCNT-1 and (d) GCNT-2

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Figure 4.5: TEM micrographs of (a) RGO (b) MWCNT (c) GCNT-1 and (d) GCNT-2

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Figure 4.6: TG traces of (a) GCNTs hybrid fillers (b) PMMA composites at 1 wt% of filler (RGO, GCNTs and CNT)

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Figure 4.7: IR spectra of (a) RGO (b) GCNT-2 (c) PMMA and (d) PMMA/GCNT nanocomposite (1 wt%)

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Figure 4.8: Raman spectra of GCNT, PMMA and PMMA/GCNT nanocomposite of varying GCNT content (1.0, 1.5 and 3.0 wt%)

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Figure 4.9: (a) TG (b) DTG traces of PMMA and PMMA/GCNT hybrid nanocomposites

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Figure 4.10: DSC scans of PMMA and PMMA/GCNT nanocomposites of varying GCNT content

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Figure 4.11: Variation of (a) storage (b) loss modulus and (c) tan delta of PMMA and PMMA/GCNT nanocomposites with temperature

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Figure 4.12: Effect of GCNT content in PMMA/GCNT nanocomposites on the electrical conductivity

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Figure 4.13: SEM micrographs of PMMA and PMMA/GCNT nanocomposites

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Figure 4.14: Plot of (a) storage modulus (Gʹ) (b) loss modulus (Gʹʹ) and (c) tan delta vs frequency for PMMA and PMMA/GCNT nanocomposites

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Figure 4.15: Plot of complex viscosity as a function of (a) angular frequency 110

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(b) GCNT content at varying frequency for PMMA and PMMA/GCNT nanocomposites

Figure 4.16: Comparison of Storage modulus (Gʹ) and loss modulus (Gʹʹ) vs frequency for the composite containing (a) 0.5 wt% (b) 2.0 wt%

of RGO and GCNT

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Figure 4.17: Complex viscosity of PMMA composite containing 0.5 wt% and 2.0 wt% of GCNT and RGO respectively

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Figure 5.1: Schematic diagram of the experimental set up of fiber optic SPR probe for ammonia gas sensing

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Figure 5.2: (a) SPR spectra for different concentrations of ammonia gas (b) variation of resonance wavelength with concentration of ammonia gas for copper and PMMA/RGO nanocomposite (5 wt%) coated fiber optic SPR probe

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Figure 5.3: (a) SPR spectra for different concentrations of ammonia and (b) variation of resonance wavelength with concentration of ammonia gas for copper and RGO coated fiber optic SPR probe

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Figure 5.4: (a) SPR spectra for different concentrations of ammonia (b) variation of resonance wavelength with concentration of ammonia gas for copper and PMMA coated fiber optic SPR probe

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Figure 5.5: Variation of total shift in resonance wavelength with RGO loadings in PMMA matrix for ammonia gas concentration ranging from 10-100 ppm for copper/(PMMA/RGO)

nanocomposite coated fiber optic SPR probe 127 Figure 5.6: Total shift in the resonance wavelength for the concentration

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range 10-100 ppm of different gases with (a) RGO and (b)

PMMA/RGO nanocomposite (5 wt%) as a sensing layer 129 Figure 5.7: (a) Total shift in resonance wavelength for ammonia gas

concentration range from 10-100 ppm and (b) variation of sensitivity with concentration of ammonia gas for three different sensing probes

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Figure 5.8: Total shift in resonance wavelength of PMMA/RGO nanocomposite (5 wt%) sensing layer for the concentration range 10–20 ppm of different gases

132

Figure 5.9: Variation of the normalized transmitted power with time as the gas is introduced and removed from the gas chamber at NH3 gas concentration 20 ppm and wavelength of light is 882 nm

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Figure 5.10: Possible interaction of NH3 molecules with RGO nanosheets 135 Figure 5.11: Schematic of fabricated probe using different sensing layers 138 Figure 5.12: (a) SPR spectra for different concentrations of methane gas (b)

variation of resonance wavelength with concentration of methane gas for silver and PMMA/GCNT hybrid nanocomposite (5 wt%) coated fiber optic SPR probe

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Figure 5.13: (a) SPR spectra for different concentrations of methane and (b) variation of resonance wavelength with concentration of methane gas for silver and RGO coated fiber optic SPR probe

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Figure 5.14: (a) SPR spectra for different concentrations of methane and (b) variation of resonance wavelength with concentration of methane gas for silver and CNT coated fiber optic SPR probe

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Figure 5.15: (a) SPR spectra for different concentrations of methane and (b) 144

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variation of resonance wavelength with concentration of methane gas for silver and GCNT coated fiber optic SPR probe

Figure 5.16: (a) SPR spectra for different concentrations of methane and (b) variation of resonance wavelength with concentration of methane gas for silver and PMMA coated fiber optic SPR probe

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Figure 5.17: Variation of total shift in resonance wavelength with GCNT loadings in PMMA matrix for methane gas concentration ranging from 10-100 ppm for silver-PMMA/GCNT hybrid nanocomposite coated fiber optic SPR probe

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Figure 5.18: Total shift in the resonance wavelength for the concentration range 10-100 ppm of different gases with (a) RGO and (b) CNT (c) GCNT and (d) PMMA/GCNT hybrid nanocomposite (5 wt%) as a sensing layer

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Figure 5.19: (a) Total shift in resonance wavelength for methane gas concentration 10-100 ppm and (b) variation of sensitivity with concentration of methane gas for different sensing probes

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Figure 6.1: Schematic for the preparation reduced graphene oxide (RGO) from graphite

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Figure 6.2: Schematic for the preparation PMMA/RGO composites by three methods using in-situ bulk polymerization technique

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Figure 6.3: Schematic for the preparation of GCNT hybrid filler 158

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List of Tables

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Table 2.1: Properties of poly(methyl methacrylate) [from supplier data sheet] 31 Table 2.2: Details of PMMA/RGO composite prepared by sheet casting method

alongwith sample designation

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Table 2.3: Details of PMMA/GCNT hybrid composite prepared by sheet casting method alongwith sample designation

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Table 3.1: Results of EDX analysis for GO and RGO 54 Table 3.3: Results of electrical conductivity for PMMA/RGO composites

prepared by different method

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Table 3.4: Results of TG traces of GO, RGO and PMMA/RGO nanocomposites in N2 atmosphere

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Table 3.5: Results of storage modulus and glass transition for PMMA/RGO composites

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Table 3.6: Mechanical properties of PMMA/RGO composites prepared by different methods

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Table 3.7: Results of crossover frequency response for PMMA and PMMA/RGO composites prepared by sheet casting

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Table 4.1: Results of electrical conductivity of PMMA composite having different fillers

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Table 4.2: Details of PMMA/GCNT hybrid composites prepared by sheet casting along with sample designation

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Table 4.3: Results of TG traces for PMMA/GCNT nanocomposites in N₂ atmosphere

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Table 4.4: Results of storage modulus and glass transition temperature for

PMMA/GCNT nanocomposites 101

Table 4.5 Results of reinforcement effectiveness parameter obtained from storage modulus vs temperature plot of PMMA/GCNT

nanocomposites 103

Studies on graphene based poly (methyl methacrylate) nanocomposites

STUDIES ON GRAPHENE BASED POLY(METHYL METHACRYLATE) NANOCOMPOSITES

SANDEEP NATH TRIPATHI

CENTRE FOR POLYMER SCIENCE AND ENGINEERING INDIAN INSTITUTE OF TECHNOLOGY DELHI

APRIL 2015

© Indian Institute of Technology Delhi (IITD), New Delhi, 2015

STUDIES ON GRAPHENE BASED POLY(METHYL METHACRYLATE) NANOCOMPOSITES

by

SANDEEP NATH TRIPATHI

Centre for Polymer Science and Engineering

submitted

in fulfilment of requirements of the degree of Doctor of Philosophy

to the

INDIAN INSTITUTE OF TECHNOLOGY DELHI

APRIL 2015

Dedicated to my parents Shri Haridwar Nath Tripathi

&

Smt. Ramrati Devi

CERTIFICATE

ACKNOWLEDGEMENTS

ABSTRACT

CONTENTS

List of Figures

List of Tables